Band tensioning system

Abstract

Belt tensioning system The invention relates to an agricultural machine comprising at least one processing unit equipped with at least one endless belt conveyor and capable of occupying a working position in which the conveyor allows a product to be moved, the belt being guided in its movement by at least two rollers guided in rotation around longitudinal axes, a tensioning system being associated with the or each belt and comprising an energy accumulator and a tensioning cylinder allowing the spacing between the longitudinal axes to be varied, to the or each belt is associated a regulation system which prevents, in the working position of the processing unit, the circulation of oil from a first line connecting the regulation system to a hydraulic distributor, towards a second line connecting the regulation system to the tensioning cylinder, when the pressure in the second line is greater than a limit value.Figure to be published with the abbreviation: Fig. 1.

Description

Description Title of the invention: Belt tensioning system The present invention relates to the field of agricultural machinery and in particular agricultural machines incorporating at least one belt conveyor for moving a product. Its subject is a machine of the aforementioned type with a conveyor whose belt tensioning means is improved. Belt conveyors, mounted on belt rakes or mowers for example, allow the movement of product in order to deposit it in the form of windrows. These windrows are arranged longitudinally to the direction of travel of the machine so that they can be easily picked up by a collecting machine, such as a baler or a forage harvester. The belt is said to be endless because it forms a closed loop. It is wound around at least two rollers. Generally, one of the rollers is the drive. One or more other rollers can be the follower(s). In order to ensure the belt drive, respectively the adhesion between the rollers and the belt, the belt must be tensioned. The belt tension can be adjusted in particular by changing the distance between two rollers, respectively by increasing or decreasing the distance between the longitudinal axes of two rollers. Insufficient belt tension increases the risk of friction between the belt and the parts located below, particularly the parts located near the middle, which is the most overhanging. Insufficient tension also risks causing the belt to slip on at least one of the rollers. The invention relates more specifically to an agricultural harvesting machine intended to be moved in a forward direction, this machine comprising at least one processing unit with at least one conveyor equipped with an endless belt, the processing unit being able to occupy a working position, in which the or each conveyor allows a product to be moved, the belt being guided in its movement by at least two rollers, each guided in rotation around a respective longitudinal axis. A tensioning system is associated with the or each belt and comprises an energy accumulator and a tensioning cylinder making it possible to vary the spacing between the longitudinal axes. A machine as previously described is disclosed in document US20170215342. In its variant of Figure 9, the web tensioning system of this machine comprises tension cylinders, for each of which the tension chamber to be supplied to tension the respective web is connected to an energy accumulator. In addition, the relaxation chamber of each tension cylinder to be supplied to relax the respective web operates in a closed circuit in the working position. However, the oil contained in this expansion chamber cannot be compressed, it cannot escape in the working position. However, it happens that the belt expands quickly following a significant increase in temperature during a day, and / or more slowly through aging. It follows from the above that if the belt of such a machine expands, the or each tension cylinder cannot lengthen. An expansion of the belt, whatever the origin, then implies a lower tension of the belt which can lead to a loss of adhesion of the belt on the rollers, or even its slipping on the rollers. This loss of grip can be gradual: the belt will initially tend to slip incidentally, without this being visible. It is only when the belt slips a lot (or is no longer driven at all) that the user is likely to notice the problem. The fact that the belt slips, even occasionally, increases the risk of product jamming at the conveyor and means a less regular windrow, which can cause complications for the windrow pick-up machine. It is therefore necessary to regularly ensure that the belt is sufficiently tensioned. In practice, experience has shown that users do not often bother to carry out this type of regular check. In addition, slipping of the belt on a roller leads to premature wear of the belt. Another disadvantage of the hydraulic circuit of Figure 9 of document US20170215342 lies in the fact that, regardless of the position of the hydraulic distributor 3-3, the pump constantly delivers oil. Pumping oil continuously, in addition to being unnecessary and putting additional strain on the pump, is not economical and results in excess fuel consumption over the entire duration of the agricultural work. Finally, oil that is continuously circulated by a pump tends to heat up, which can lead to a deterioration of its properties and a reduction in the machine's efficiency. According to the embodiments of Figures 10 and 11 of document US20170215342, in the working position of the machine, in order to tension the respective strip, each of the chambers of the tensioning cylinders is connected to an additional energy accumulator so that the tension of the strip or strips remains constant, even after expansion. Furthermore, a constant oil supply is not necessary, at least not in the working position. Document US20170215342 thus makes it possible, through the embodiments of [Figures 10 and 11, to ensure a strip tensioning system with lower energy consumption. A major disadvantage of these embodiments, however, is the number of hydraulic components required, more precisely the number of accumulators and cylinders, including double-acting cylinders, and consequently of hydraulic connections.Such a hydraulic circuit is complex and has significant production, operating and maintenance costs. Finally, the accumulators. Energy generators are subject to special rules when transporting them in containers, increasing the transport cost of such a machine. The present invention aims to overcome at least one of the drawbacks of the aforementioned known solution. To this end, it relates to a machine of the type mentioned in the introduction, characterized in that it comprises a hydraulic regulation system which prevents, at least in the working position of the treatment unit concerned, the circulation of oil from a first pipe connecting the regulation system to a hydraulic distributor, in the direction of a second pipe connecting the regulation system to the tension cylinder, when the pressure in the second pipe is greater than a limit value, and in that the accumulator is connected to the second pipe. The invention will be better understood from the following description, which relates to a preferred embodiment, given by way of non-limiting example, and explained with reference to the appended schematic drawings, in which: [Fig.1] represents two examples of agricultural machines covered by the invention, a first machine comprising two processing units and being attached to the rear of a tractor, and a second machine attached to the front of the tractor; [Fig.2a] schematically represents a hydraulic circuit of a machine according to the invention, this circuit being connected to the hydraulic circuit of a tractor, the machine comprising a treatment unit in working position (distributor in floating position); [Fig.2b] schematically represents a hydraulic circuit of a machine according to the invention comprising two processing units, each comprising a tensioning cylinder for the respective belt, the hydraulic circuit of the machine being connected to the hydraulic circuit of a tractor; [Fig.3] is a perspective view of a processing unit which may be part of one of the machines of [Fig.1] and [Fig.5]; [Fig.4] is a perspective view of a conveyor which may form part of the processing unit of [Fig.3], the belt having been obscured in order to better see the frame; and [Fig.5] is a schematic perspective view of a machine according to the invention intended to be mounted at the rear of an agricultural tractor and comprising two processing units, only one unit being shown. [Fig. 1] illustrates two agricultural harvesting machines (1) coupled to a tractor (T). Each agricultural machine (1) is intended to be moved in a forward direction (A). Each machine (1) comprises at least one processing unit (3). Each processing unit (3) is equipped with at least one endless belt (5) conveyor (4). The processing unit (or each unit) (3) can occupy a working position in which the or each conveyor (4) allows a product to be moved. Most often, the product is a loose plant product, such as straw or cut grass. The belt (5) is guided in its movement by at least two rollers (8, 8'). At least during this movement, the belt (5) forms an orbit. Each roller (8, 8”) is guided in rotation about a respective longitudinal axis (12, 12°). A tensioning system (6) is associated with the (or each) strip (5). The tensioning system (6) comprises at least one energy accumulator (21). The accumulator (21) is preferably a container in which the volume of oil it contains can vary. It is preferably hydropneumatic. The tensioning system (6) also comprises (at least) one tensioning cylinder (9) for varying the spacing between the longitudinal axes (12, 12”). The tensioning cylinder (9) has a tensioning chamber (13). In order to tension the respective strip (5), the tensioning chamber (13) is supplied with oil. When the tensioning chamber (13) is supplied with oil, for example when it is connected to a pump (P), the tensioning cylinder (9) moves the longitudinal axes (12, 12”) away from the respective rollers (8, 8), preferably by extending. The agricultural machine (1) is preferably intended to be coupled to an agricultural tractor (T). The tractor (T) makes it possible to move the machine (1) in the forward direction (A). The machine (1) thus preferably comprises at least one coupling frame intended to be connected to the coupling device of the tractor (T). The coupling device of the tractor (T) can be rear or front. Preferably, a power take-off of the tractor (T) makes it possible to drive the machine (1), respectively its or each processing unit (3). The machine (1) could however be self-propelled. The machine (1) also comprises a chassis (22). This chassis (22) connects the coupling frame to the or each processing unit (3). The machine (1) also comprises at least one hydraulic circuit (47) for controlling at least certain functions. These functions are, for example, tensioning the belt (5), transposing the or each processing unit (3) between its working, circulation and / or transport positions, or even rotating a roller (8) in order to set the belt (5) in motion. etc. The tractor (T) also comprises its own hydraulic circuit (18). The hydraulic circuit (18) of the tractor (T) comprises at least one pump (P), a reservoir (R) and at least one hydraulic distributor (17). The hydraulic circuit (18) of the tractor (T) can be connected to the hydraulic circuit (47) of the machine (1), as illustrated in Figures 2.A pump (P), a reservoir (R) and a distributor (17) can also be included in the hydraulic circuit (47) of the machine (1), in particular in the case of a self-propelled machine (1). As illustrated in [Fig. 3], the or each processing unit (3) may comprise a harvesting device (14) located, in the working position, in front of the conveyor (4) in the direction of advance (A). The harvesting device (14) moves the product towards the conveyor (4). In the preferred embodiment of [Fig. 3], the harvesting device (14) is a pickup comprising a drum (35) equipped with raking teeth. The drum (35) can be rotated about a substantially horizontal axis orthogonal to the direction of advance (A) in order to pick up the product cut from the ground (S). In an alternative embodiment, the harvesting device (14) is a mowing bar which cuts the product still standing before transferring it to the conveyor (4). The machine (1) is thus a mower and / or a belt rake (5). According to the invention, the or each belt (5) is associated with a hydraulic regulation system (10) which prevents, at least in the working position of the treatment unit (3) concerned, the circulation of oil from a first line (31) connecting the regulation system (10) to a hydraulic distributor (17), towards a second line (32) connecting the regulation system (10) to the tensioning cylinder (9), when the pressure in the second line (32) is higher than a limit value. Still according to the invention, the accumulator (21) is connected to the second line (32). Thanks to these arrangements, the tensioning system (6) operates in a closed circuit as long as the pressure in the second line (32) is higher than the limit value, allowing the accumulator (21) to compensate for both a retraction and an expansion of the belt (5). The belt (5) is in fact flexible. Its flexibility is influenced in particular by the temperature.The strip (5) may in particular be made of elastomer and / or rubber. When the pressure in the second line (32) is lower than the limit value, the control system (10) allows the circulation of oil from the first line (31) towards the second line (32). Thus, the pump (P) is only used to tension the band (5) if necessary, advantageously reducing the energy consumption of the machine (1), and making its use more economical. By "if necessary" is meant if the pressure in the second line (32) is lower than the limit value. Also, the oil in the hydraulic circuit (47) of such a machine (1) is less likely to heat up, due to this circulation as needed. In addition, the hydraulic circuit (47) of the machine (1) is simple to produce. In fact, the regulation system (10) comprises a limited number of hydraulic components, in particular accumulators and cylinders, advantageously reducing the cost price and the maintenance cost of the machine (1). In the preferred embodiment, the or each tensioning system (6) in fact comprises a single accumulator @l). [Fig. 1] illustrates precisely two agricultural harvesting machines (1). A first machine (1) is mounted at the front of a tractor (T). It is equipped with a single processing unit (3). A second machine (1) is mounted at the rear of the tractor (T). This is equipped with two processing units (3). Each processing unit (3) may comprise one or more endless belt (5) conveyor(s) (4). In the preferred embodiment, each conveyor (4) makes it possible to move the product transversely to the direction of advance (A).By advancing the machine (1) and moving the product by the conveyor (4) transversely to the direction of advance (A), at least one windrow (25) is formed. The windrow (25) is the product deposited by the machine (1), respectively by the conveyor (4), on the ground (S). The windrow (25) is thus longitudinal to the direction of advance (A). In the working position of the processing unit (3) concerned, the driving of the belt (5) of the or each conveyor (4) around its respective orbit allows the product to be moved. When the belt (5) is guided by only two rollers (8, 8'), the orbit of the respective belt (5) is preferably oblong in shape, seen along one of the longitudinal axes (12, 12”). The or each processing unit (3) can also occupy a circulation position in which the conveyor (4) is further from the ground (S) than in the working position.At least in the case of a machine (1) to be coupled to the rear of the tractor (T), the processing unit (3) can also occupy a transport position, in which its horizontal dimension and perpendicular to the direction of travel (A) is reduced compared to that in the working position. In order to drive the belt (5), at least one of the rollers (8, 8') is driven. A hydraulic motor (26) is used to drive the driven roller (8, 8') in rotation about the respective longitudinal axis (12, 12'). The hydraulic motor (26) thus drives the belt (5). Changing the direction of rotation of the hydraulic motor (26) thus changes the direction of movement of the belt (5). Each conveyor (4) can deposit a swath (25) on one side or the other of the processing unit (3), seen along the direction of advance (A). Depending on the direction of rotation of the belt (5), the swath (25) can be deposited on one side or the other of the processing unit (3). In the case of a processing unit (3) comprising two conveyors (4), two windrows (25) can also be deposited, each on either side of the processing unit (3).According to an alternative embodiment, the machine (1) can have two processing units (3) or two conveyors (4) movable transversely to the direction of advance (A). A single swath (25) can then be produced between the two conveyors (4). When the machine (1) is connected to the rear of the tractor (T), the swath (25) is deposited, as desired, towards the chassis (22) and / or on the side opposite the chassis (22). In some applications, the belt (5) may also be guided by three or more rollers (8, 8'). In top view and in the working position of the processing unit (3), each longitudinal axis (12, 12°) is preferably substantially parallel to the direction of advance (A), maximizing the working width of the conveyor (4). As shown in Figures 2, the hydraulic distributor (17) allows connect the first line (31) to the pump (P) and / or to the reservoir (R). Although the second line (32) connects the regulation system (10) to the tension cylinder (9), it is however possible for another hydraulic element to be mounted between the regulation system (10) and the tension cylinder (9). For example, in an alternative embodiment not shown, a non-return valve is mounted on the second line (32) between the regulation system (10) and the tension cylinder (9). In the same way, it remains conceivable for hydraulic elements to be mounted on the first line (31). Thus, as shown in [Fig.2b], the first line (31) connects the regulation system (10) to the distributor (17) via a selection valve (43) and a restriction valve (36) (detailed later). The distributor (17) is for example of type 3-3 (with three inlets and three configurations), or 4-4 (with four inlets and four configurations). The distributor (17) can occupy at least one closed configuration in which it prevents any circulation of oil towards the first pipe (31). The distributor (17) can also occupy a floating configuration in which it connects the first pipe (31) to the tank (R). The configurations of the distributor (17) can be modified manually, preferably from the tractor cab (T). According to another interesting characteristic, a hydraulic receiver (19) is associated with the or each band (5). This hydraulic receiver (19) is connected to the first pipe (31). As can be seen from Figures 2, the hydraulic receiver (19) is preferably connected to the first pipe (31) by a third hydraulic pipe (33). The hydraulic receiver (19) performs a function other than the tensioning system (6) of the band (5). Connecting a hydraulic receiver (19), respectively the third pipe (33), to the first pipe (31) makes it possible to simplify the hydraulic circuit (47) of the machine (1), by reducing the number of pipes and / or the total length of the pipes. This also makes it possible to use a single distributor to perform several functions. The hydraulic receiver (19) is thus part of the hydraulic circuit (47) of the machine (1). It is clear from [Fig. 2a] in particular that the second line (32) connects at least the tension chamber (13) and the control system (10). The pressure in the tension chamber (13) is identical to the pressure in the second line (32). Preferably, the second line (32) also connects the control system (10) and the accumulator (21). The pressure in the tension chamber (13) is also identical to the pressure in the accumulator (21) (oil side). By means of the control system (10) as proposed above, the pressure in the second line (32) is increased up to the limit value, if necessary, each time the hydraulic receiver (19) is supplied with oil, respectively each time the hydraulic receiver (19) is connected to the pump (P). Thus, the band (5) is re-tensioned, if necessary, each time that the hydraulic receiver (19) is supplied with oil, further reducing the risk of slackening of the belt (5). Furthermore, when the pressure in the second line (32) is higher than the limit value, the hydraulic receiver (19) can be supplied with oil without the second line (32) being supplied with oil. The hydraulic receiver (19) can thus be actuated without the tension of the belt (5) being changed. The hydraulic receiver (19) may in particular comprise at least one hydraulic motor and / or at least one hydraulic cylinder. When the hydraulic receiver (19) comprises at least one hydraulic motor constantly connected to the pump (P) during use of the machine (1), the tension of the belt (5) is increased as soon as the pressure in the second line (32) falls below the limit value. The belt (5) cannot therefore be slackened in the working position. In an alternative embodiment not shown, the hydraulic receiver (19) is produced by the hydraulic motor (26). Preferably, the hydraulic motor (26) makes it possible to drive the respective belt (5) around its orbit. Alternatively, the hydraulic motor (26) makes it possible to drive the mower bar of the harvesting device (14). The hydraulic motor (26) could also drive at least one wheel of a self-propelled vehicle. In the preferred embodiment, the hydraulic receiver (19) comprises at least one lifting cylinder (7). The lifting cylinder (7) makes it possible to transpose the associated processing unit (3) between its working position and its circulation position. The lifting cylinder (7) being used at least each time the machine (1) is used, the tension of the strip (5) is automatically updated at least before each use, thus reducing the attention that the user must pay to regularly checking the tension of the strip (5). In practice, the or each lifting cylinder (7) is used at each half-turn, at the headland and each time a swath (25) is crossed during the advance of the machine (1). Given the frequency with which the strip (5) is then re-tensioned if necessary, visually checking the tension of the strip (5) is therefore not necessary.Indeed, a major disadvantage of known machines of this type is that the user must regularly remember to ensure that the tension of the belt (5) is sufficient, visually. In addition, it is not uncommon for the user to forget to check whether the tension of the belt (5) is sufficient. If the tension of the belt (5) is insufficient, it may also be necessary to re-tension the belt (5), wasting even more time for the user. As shown in [Fig. 1], the machine (1) may comprise two processing units (3). As shown in [Fig. 5], at least one of the processing units (3) may be movable transversely to the direction of advance (A). Preferably, each processing unit (3) and / or conveyor (4) is associated with at least one transverse cylinder (28) making it possible to move the associated processing unit (3) and / or the conveyor (4) associated transversely, and preferably perpendicularly, to the direction of advance (A). Alternatively or additionally, the hydraulic receiver (19) may comprise a transverse cylinder (28). When the or each band (5) is associated with a hydraulic receiver (19) connected to the first pipe (31), when this hydraulic receiver (19) requires the floating configuration of the distributor (17) in the working position of the treatment unit (3) concerned, and when the pressure in the second pipe (32) is lower than the limit value, the oil can flow from the second pipe (32) to the reservoir (R), causing the band (5) to relax. In order to avoid the band (5) relaxing in this case, the or each band (5) is associated with a non-return valve (38) mounted so as to prevent the flow of oil from the second pipe (32) to the respective first pipe (31). Thanks to the non-return valve (38), when the hydraulic receiver (19) comprises at least one lifting cylinder (7), the treatment unit (3) concerned can thus follow the unevenness of the ground (S) without the belt (5) risking slackening. In the preferred embodiment, the control system (10) comprises at least one pressure regulator (11). The control system (10) thus prevents, at least in the working position of the relevant processing unit (3), the flow of oil towards the second line (32) when the pressure in the second line (32) is higher than the limit value. Specifically, the control system (10) prevents the flow of oil from the first line (31) to the second line (32) when the pressure in the tension chamber (13) is higher than the limit value, regardless of the position of the relevant processing unit (3). By means of the pressure regulator (11), the control system (10) additionally permits, at least in the working position of the relevant processing unit (3), the flow of oil towards the tension chamber (13) when the pressure in the tension chamber (13) is lower than the limit value.The user can thus tension the band (5) simply by connecting the first line (31) to the pump (P). Preferably, the limit value is adjustable at the pressure regulator (11), allowing it to be adapted to the characteristics of the band (5), the tensioning cylinder (9), and / or the accumulator (21). When the pressure in the second line (32) is higher than the limit value, a three-way pressure regulator (11) sends the oil from the second line (32) to a or the reservoir (R). With a three-way pressure regulator (11), it is then necessary that the limit value is higher than the pressure required to supply the hydraulic receiver (19). Otherwise, the hydraulic receiver (19) cannot be actuated. Furthermore, if the limit value is higher than the pressure required to actuate the hydraulic receiver (19), when the hy- hydraulic (19) no longer requires an oil supply and the pressure in the second line (32) is higher than the limit value, then the pump (P) is connected to the reservoir (R), involving higher energy consumption and a risk of heating the oil. The pressure regulator (11) is therefore preferably of the two-way type. In other words, the pressure regulator (11) is not directly connected to one or to the reservoir (R). The control system (10) may also comprise a pressure limiter (40) connected to the or a reservoir (R) so as to prevent the circulation of oil towards the second pipe (32), when the pressure in this second pipe (32) is higher than a set value. Such a control system (10) ensures that the tension of the band (5) cannot be such that it would cause a distension of the band (5). The set value is preferably adjustable at the pressure limiter (40). With a control system (10) comprising a pressure limiter (40) and no pressure regulator (11), the set value is preferably higher than the pressure necessary to actuate the hydraulic receiver (19), so that this hydraulic receiver (19) can be actuated. In the case where the regulation system (10) comprises a pressure limiter (40) and a pressure regulator (11), the set value of the pressure limiter (40) is preferably greater than the limit value of the pressure regulator (11), in order to allow the pressure regulator (11) to block the circulation of oil from the first pipe (31) towards the second pipe (32). In the case where the regulation system (10) comprises a pressure limiter (40) and a pressure regulator (11), and the hydraulic circuit (47) of the machine (1) comprises a hydraulic receiver (19), the pressure regulator (11) is preferably mounted between the non-return valve (38) and the pressure limiter (40) so that the pressure limiter (40) makes it possible to limit the pressure in the second pipe (32), regardless of the position of the pressure regulator (11). In order to simplify the hydraulic circuit (47) of the machine (1), as well as its use, by reducing the number of adjustments, the regulation system (10) preferably does not include a pressure limiter (40). Also in order to simplify the hydraulic circuit (47) of the machine (1), the or each regulation system (10) comprises a single pressure regulator (11). In order to allow relaxation of the or each belt (5), in particular in the transport position of the treatment unit (3) concerned, a stop valve (30) is mounted in parallel with the or each non-return valve (38). This stop valve (30) is closed in the working position of the treatment unit (3) concerned. Opening this stop valve (30) allows oil to be released from the tensioning system (6), thus relaxing the belt (5) and preventing it from deforming under the effect of tension over a prolonged period. It It is therefore recommended to release part of the pressure from the tension cylinder (9) when the treatment unit (3) is in the transport position. The shut-off valve (30) and / or the non-return valve (38) are preferably mounted between the regulation system (10) and the first pipe (31) in order to ensure that the pressure measured by the pressure regulator (11) and / or the pressure limiter (40) is identical to the pressure in the second pipe (32). As illustrated in [Fig.4], each roller (8, 8') is pivotally mounted with a frame (16) about its respective longitudinal axis (12, 12”). The frame (16) is preferably part of the conveyor (4). In order to adapt to the different spacings between the longitudinal axes (12, 12”) of the rollers (8, 8°), the frame (16) comprises a main part (23) and a carriage (24). The carriage (24) is movable relative to the main part (23) transversely to the longitudinal axes (12, 12”). On the main part (23) is mounted a roller (8, 8°) and on the carriage (24) the other roller (8, 8°). Preferably, a roller (8°) called fixed is mounted on the main part (23), and a roller (8) called mobile on the carriage (24). Preferably, the motor roller (8, 8') for driving the strip (5) around its orbit is the fixed roller (8°). The carriage (24) is guided in translation relative to the main part (23). The carriage (24) is thus mounted with the ability to slide relative to the main part (23) parallel to the plane passing through the longitudinal axes (12, 12”) of the rollers (8, 8'), thus allowing the variation of the spacing between the longitudinal axes (12, 12°). The tension cylinder (9) is connected on the one hand to the carriage (24) and on the other hand to the main part (23), thus being able to modify the spacing between the longitudinal axes (12, 12'), respectively between the rollers (8, 8°). Preferably, a crosspiece (27) is pivotally mounted with the main part (23) along a main axis (29). The main axis (29) is perpendicular to the plane passing through the longitudinal axes (12, 12”) of the rollers (8, 8'). The crosspiece (27) is pivotally mounted with the tension cylinder (9), preferably along an axis parallel to the main axis (29). The crosspiece (27) is also pivotally mounted with the carriage (24), preferably along an axis parallel to the main axis (29). Finally, the tension cylinder (9) is articulated with the carriage (24), preferably along an axis parallel to the main axis (29). The main axis (29) is preferably located substantially in the middle of the width of the conveyor (4), making it possible to substantially halve the force required to be generated by the tension cylinder (9) to move the carriage (24) and tension the belt (5). Given the often limited spacing between the two sides of the strip (5), and in order to facilitate its assembly and maintenance, it may be provided that the tension cylinder (9) is located outside the volume delimited by the strip (5). Access to the tension cylinder (9) is thus facilitated and an oil leak at the hydraulic circuit (47) of the machine (1) presents less risk of reducing the adhesion between the belt (5) and the roller(s) (8, 8°), avoiding slippage of the belt (5). The or each tension cylinder (9) is preferably single-acting, simplifying the hydraulic circuit (47) of the machine (1). Alternatively, the or each tension cylinder (9) is double-acting, the tension chamber (13) being connected to the second pipe (32) and the other chamber to the air by a breather (37). Preferably, the or each tension cylinder (9) is linear in operation, simplifying the kinematics of the machine (1). Alternatively, it may be provided that the control system (10) comprises an electronic system with a pressure sensor measuring the pressure in the second line (32), and that this electronic system makes it possible to open and close a valve each time the pressure in the second line (32) falls below, or rises above, the limit value. Such a control system (10) would, however, be more complex and would have a higher cost price. [Fig. 5] represents a machine (1) which may comprise several processing units (3). In order to ensure the orientation of the processing unit (3) during its transpositions between working and circulation positions, preferably substantially parallel to the ground (S), in the preferred embodiment of [Fig. 2b], the hydraulic receiver (19) is composed of two lifting cylinders (7). Preferably, the lifting cylinders (7) are connected in series. In the example of [Fig. 5], the lifting cylinders (7) make it possible to pivot the processing unit (3) around at least one axis which is substantially horizontal and substantially perpendicular to the direction of advance (A), and preferably located at the rear of the associated conveyor (4). The third hydraulic line (33) is preferably connected to a lifting chamber (39) of the or each lifting cylinder (7). Supplied with oil, the lifting chamber (39) allows the associated treatment unit (3) to be transposed from its working position to its circulation position. To move from the circulation position to the working position, the weight of the treatment unit (3) allows it to be lowered into the working position. Thus, to move from the circulation position to the working position, the lifting chamber (39) of each lifting cylinder (7) can be simply connected to the reservoir (R). It is clear from the above that the or each lifting cylinder (7) is preferably single-acting, simplifying the hydraulic circuit (47) of the machine (1) and reducing its energy consumption. Preferably, the distributor (17) can also occupy a filling configuration in which it allows the pump (P) and the first pipe (31) to be connected. In the filling configuration, the distributor (17) allows, when the hydraulic receiver (19) comprises at least one lifting cylinder (7), to transpose the unit of treatment (3) between working and circulation positions. In the circulation position, the distributor (17) is in the closed position in order to maintain (in height) the treatment unit (3). On the machine (1) of [Fig. 5], the or each processing unit (3) is associated with a transport cylinder (42) making it possible to transpose the processing unit (3) in question into the transport position. A processing unit (3) can reach its transport position from its working position and / or its circulation position. In this exemplary embodiment, in the transport position, the longitudinal dimension of the processing unit (3) is substantially parallel to the direction of advance (A), and preferably substantially horizontal. The transport position may however be identical to the circulation position, in particular in the case of a frontal machine (1) as shown in [Fig. 1] at the front of the tractor (T). As can be seen from [Fig. 2b], in order to reduce the number and / or length of the hydraulic lines of the machine (1), it may be provided that the or each transport cylinder (42) is connected to the associated first line (31) by a sixth line (46). The transport cylinder (42) preferably being double-acting, a first chamber of the transport cylinder (42) is connected to the first line (31) by the sixth line (46). The other chamber of the transport cylinder (42) is connected to the distributor (17) by a fifth line (45). In the preferred embodiment of [Fig.2b], in order to be able to transpose a treatment unit (3) into the working or circulation position independently of the other treatment unit (3) of the machine (1), a selection valve (43) is associated with each treatment unit (3). Each selection valve (43) is preferably operable from the tractor (T). Each selection valve (43) is of the 4-2 type, with 4 outlets and 2 positions. Still according to the preferred embodiment of [Fig.2b], a balancing valve (44) is mounted at the terminals of the or each transport cylinder (42), in particular to prevent the weight of the or each treatment unit (3) from causing it to be transposed to the working position during transport, in particular in the case where the transport cylinder (42) is accidentally connected to the tank (R), or in the case of a significant hydraulic leak. In order to ensure the sequencing of the actuation of the transport (42) and lifting (7) cylinders during transpositions between working and transport positions, a restriction valve (36) is mounted on the first pipe (31). Preferably, the restriction valve (36) is mounted between the intersection of the first pipe (31) with the third pipe (33) and the intersection of the first pipe (31) with the corresponding sixth pipe (46). Preferably, the restriction valve (36) is mounted on the machine (1) so as to detect whether the associated processing unit (3) is in circulation position. When the associated treatment unit (3) is not in the working position, in particular when it is in the transport or circulation position, the restriction valve (36) prohibits the circulation of oil from the lifting (7) and tensioning (9) cylinders to one or the tank (R). When a treatment unit (3) is in the working position, the restriction valve (36) allows any circulation of oil between the distributor (17) and the associated lifting (7) and tensioning (9) cylinders. In this way, with the distributor (17) in the floating position, it is possible to operate the machine (1) with one treatment unit (3) in the working position and the other treatment unit (3) in the circulation position. In order to control the pressure in the tension cylinder (9), a pressure gauge (34) can be connected to the second line (32). Of course, the invention is not limited to the embodiment described and shown in the attached drawings. Modifications remain possible, particularly from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

Claims

1. Agricultural harvesting machine (1) intended to be moved in a direction of advance (A), the machine (1) comprising at least one unit treatment (3) equipped with at least one conveyor (4) with belt (5) without end, the processing unit (3) being able to occupy a working position in which the or each conveyor (4) allows a product to be moved, the strip (5) being guided in its movement by at least two rollers (8, 8'), each guided in rotation around a longitudinal axis (12, 12') respectively, a tensioning system (6) being associated with the or each strip (5) and comprising an energy accumulator (21) and a tension cylinder (9) allowing the spacing between the axes to be varied longitudinal (12, 12°), agricultural machine (1) characterized in that at the or each band (5) is associated with a hydraulic regulation system (10) which prevents, at less in working position of the processing unit (3) concerned, the cir- oil flow from a first pipe (31) connecting the system of regulation (10) to a hydraulic distributor (17), in the direction of a second line (32) connecting the regulation system (10) to the cylinder of tension (9), when the pressure in the second line (32) is su- greater than a limit value, and in that the accumulator (21) is connected to the second pipe (32).

2. Agricultural machine according to claim 1, characterized in that at the or each band (5) is associated with a hydraulic receiver (19) connected to the first line (31).

3. Agricultural machine according to claim 2, characterized in that the hydraulic receiver (19) is made by a hydraulic motor (26) allowing the belt to be driven (5).

4. Agricultural machine according to claim 2, characterized in that the hydraulic receiver (19) comprises at least one lifting cylinder (7) which allows the associated processing unit (3) to be transposed between its working position and its circulation position in which the conveyor (4) is further from the ground (S) than in the working position.

5. Agricultural machine according to any one of claims 1 to 4, ca- characterized in that the or each band (5) is associated with an anti-valve return (38) mounted so as to prevent the circulation of oil from the second conduit (32) to the first conduit (31) respectively.

6. Agricultural machine according to any one of claims 1 to 5, ca- characterized in that the regulation system (10) comprises at least one pressure regulator (11).

7. Agricultural machine according to claim 6, characterized in that the regulation system (10) does not include a pressure limiter {40).

8. Agricultural machine according to any one of claims 5 to 8, ca- characterized in that a stop valve (30) is mounted in parallel with the or of each non-return valve (38).

9. Agricultural machine according to claims 6 and 8, characterized in that the stop valve (30) and / or the non-return valve (38) are mounted between the regulator (11) and the first pipe (31).

10. Agricultural machine according to any one of claims 1 to 9, ca- characterized in that the or each tension cylinder (9) is single-acting.